The invention relates to a fuel injection pump for internal combustion engines having a rotating distribution piston which, acting within a cylinder, periodically connects the pump's working or pressure chamber during the suction stroke through radial apertures in its circumference with several fuel channels in the cylinder wall, at a rate dependent upon its rotational speed.
It is well known that any "harmful space" or "deadspace" in a pump pressure chamber i.e., the volume remaining in the pressure chamber at the top dead center of the pump piston becomes especially detrimental to the proper control of the fuel quantity to be injected, whenever the dead space is relatively large with regard to the injected fuel quantity. Consequently, the dead space is especially detrimental at low engine revolutions. Particularly at low engine revolutions, however, it is required that only minor variations in the metered fuel quantity occur, in order to achieve a quiet running of the engine on the one hand, and a favorable composition of the exhaust gases on the other hand. Where pumps are regulated by suction throttle, the effect is due to the fluid volume between the suction throttle and the pump pressure chamber.
In the injection pumps of today's generally fastturning diesel engines, it is essential, due to the high revolutions, that the cross-sectional opening between the suction line and the pump pressure chamber be large, so as to obtain an effective cross-sectional opening at high revolutions, of sufficient duration to fill the pump working chamber during the suction stroke. For this very reason, a well-known fuel injection pump design incorporates, respectively, twice as many radial apertures in its pump piston as the number of engine cylinders supplied with fuel by the injection pump. In each instance, two bores, arranged axially, one above the other in the pump piston, together work in conjunction with a longitudinal groove in the cylinder bushing of the injection pump. However, these longitudinal grooves lead directly and independently into the fuel suction chamber of the injection pump, resulting in an admittedly very favorable effective cross-sectional opening, but rendering it impossible to influence any part of the suction fuel flow by any simple means.